Pipelines for the transport of hydrocarbons, e.g. oil or gas, are typically laid along the seabed using a laying vessel. Such subsea pipelines can be installed between, for example, two subsea structures, where the subsea structures may be “christmas trees”, riser bases, Blowout Preventers (BOPs), or some other structures. Often one or both ends of the pipeline are connected (or “tied-in”) to a subsea structure using a separate jumper or spool. The extra components and procedures associated with the use of separate jumpers or spools result in high costs for the installation process. Direct tie-in methods can also be used and are often preferable. These methods include:                direct pull-in (FIG. 1), in which an end of the pipeline is pulled close to the subsea structure using a winch location on the laying vessel, and the tie-in is completed using a remotely operated vehicle (ROV) and alignment apparatus;        deflect to connect (FIG. 2), in which a wire is attached to the end of the pipeline, where the wire is routed through the subsea structure to a winch, and the wire is used to pull the subsea end of the pipeline directly to the subsea structure; and        connect and lay-away (FIGS. 3 and 4), in which the subsea end of the pipeline is connected to the subsea structure at the surface, and the subsea structure is then lowered to the seabed before the laying vessel lays the pipeline by stepping away from the subsea structure.        
A typical approach to pipelaying will involve careful design of the subsea structure and of the pipeline configuration in order to ensure that, when laid, the tie-in end of the pipeline is in the correct location and orientation with respect to the connector on the subsea structure. During the direct tie-in process, a very high tensile force is applied to the end of the pipeline, putting the pipeline under tension, in order to bring the end of the pipeline up to the connection point and complete the tie-in process. One of the reasons to put the installed pipe under tension is in order to allow for subsequent thermal expansion of the pipe that can occur during use. Without such tension, a pipeline may buckle as a result of the thermal expansion.
The forces applied to the pipeline during direct tie-in can be very high indeed. This makes high demands of the installation equipment and pipeline structure. Furthermore, at least in the absence of some compensating mechanism, the forces can cause damage to the pipeline and to the connector on the subsea structure.